Vibrating ball mill with greater amplitude of vibration at feed end



Jan. 14, 1958 cs. D. BECKER 2,319,849

VIBRATING BALL MILL WITH GREATER AMPLITUDE 0F VIBRATION AT FEED END Filed Oct. 4, 1954 United States VIBRATING BALL MILL WITH GREATER AMPLI- TUDE OF VIBRATION AT FEED END George D. Becker, Wauwatosa, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application October 4, 1954, Serial No. 459,939 3 4 Claims. 01. 241-175 The present invention relates to material comminuting mills of the type known as ball mills in which materials are comminuted in a moving container by the action of loose grinding bodies to which motion is imparted by movement of the container. The invention also relates to a method of grinding in which vibrational forces are utilized.

Mills in which a container is rotated on a horizontal axis are known as rotating ball mills. Mills in which a non-rotatable container is given a vibrational movement in a closed circular path are known as vibrating ball mills.

In vibrating ball mills the container may be considered as gyrating or vibrating without rotating. The material to be ground and the grinding bodies within the container are given a circulatory or rolling tumbling movement within and relative to the container or shell of the mill by the effect of friction between the inside wall of the container and the material or bodies in direct contact therewith. It has been found desirable in loose body milling to have large grinding bodies act upon large particles of the material being ground and smaller grinding bodies act upon the smaller partially ground particles. That is, the efficiency of the mill will be improved if grinding bodies of different sizes are used and the grinding bodies are segregated so that larger ones remain near the feed entrance portion of the mill while the smaller grinding bodies remain near the discharge of the mill.

The present inventor has found that this effect can be achieved in a vibrating ball mill if the mill is given a greater amplitude, or radius of gyration, at one end than the other; that is, if the motion is such that one point of the longitudinal axis of the container remains fixed in space while another traces a closed circular path so that the axis generates a conical surface.

Movement of a container in such a manner can be achieved by many simple mechanisms and one form of such a mechanism is described below in combination with other suitable structure to obtain the desired result.

A main object of the invention is to provide a vibrating type ball mill in which grinding bodies of different sizes are caused to segregate so that the larger bodies tend to gather at the feed end of the mill and the smaller grinding bodies tend to gather at the discharge end of the mill.

Another object of the invention is to provide a method of grinding materials by the action of loose grinding bodies in which centrifugal forces are applied in a manner so as to segregate the grinding bodies so that the larger bodies act on the larger particles of the material to be ground and the smaller bodies subsequently act on the smaller or partially reduced particles of the material.

Other objects will become apparent from the following detailed description of the invention and the accompanying drawing which shows one embodiment of the invention.

2,819,849 Patented Jan. 14, 1958 In the drawing:

Fig. 1 is a vertical sectional view through the longitudinal axis of a vibrating ball mill embodying the present invention; and

Fig. 2 is a cross sectional view taken on line II--II of Fig. 1.

Referring to Figs. 1 and 2, a suitably shaped container 10, shown as having a cylindrical shape and having end walls 11 and 12, is suspended by cables 13 from a stationary overhead supporting structure 14. The longitudinal axis 24 of container 10 extends in a horizontal direction. Resilient means such as springs 15 are provided between cables 13 and supporting structure 14 to allow container 10 to have a vibrational movement in any direction relative to supporting structure 14.

End walls 11 and 12 are provided with suitably positioned bearing housings 20 and 21 in which bearings 22 and 23 are mounted, the illustrated position being in coaxial relation to the longitudinal axis 24 of container 10. Rotatably journaled in bearings 22 and 23 is a shaft 25 with the axis thereof being coincident with the longitudinal axis 24 of container 10. Suitable sealing means 30 and 31 are provided, respectively, between shaft 25 and bearing housings 20 and 21. A protective tube 26 surrounding shaft 25 extends between walls 11 and 12 of container 10.

Weight means 32 and 33 are rigidly attached at opposite ends of shaft 25, and each of the weight means has a center of gravity disposed eccentrically of the axis of shaft 25 and the longitudinal axis 24 of container 10. However, weights 32 and 33 may be identical and located at different distances from the center of gravity of the mill including its charge, or else weight means 32 may have a larger moment of inertia than weight means 33. Weight means 32 and 33 are mounted in phase with each other and, upon rotating shaft 25, the centrifugal forces imparted to shaft 25 by weight means 32 and 33 are transmitted through bearings 22 and 23 so as to cause container 10 to vibrate.

A motor 34 mounted on a stationary support 35 is provided for driving shaft 25 of the vibrating ball mill. As the container 10 of the mill is vibratable relative to motor 34, a flexible coupling 36 is provided between shaft 40 of the motor and shaft 25 of the mill.

A feed inlet 41 and a discharge outlet 42 are provided. Means for feeding the material to be ground to the mill such as a hopper 43 is also provided and material to be ground is continuously fed to the mill through inlet 41 and ground material is continuously withdrawn from the mill through discharge opening 42.

Discharge outlet 42 may have any suitable position and, as shown in the illustrated embodiment of the invention, the discharge outlet is at the top of container 10. This arrangement is suitable for the dry grinding of materials. Suction means (not shown) are normally provided for withdrawing the ground product from the mill through discharge outlet 42. For wet grinding of materials where the material to be ground is fed to container 10 in the form of a slurry, a suitable position for discharge outlet 42 is at the bottom at one end of container 10 and a suitable perforate diaphragm would be provided in a known manner. The present invention is applicable, however, regardless of whether the mill is constructed for wet or dry grinding operations.

In accordance with the invention the effective weight of weight means 32 at the feed end of the mill, with regard to the action of centrifugal force thereon, is larger than the effective weight of weight means 33 at the discharge end of the mill. With this arrangement the centrifugal force imparted to container 10 is greater at the feed end than the discharge end of the mill so that the axis of shaft 25 and the longitudinal axis 24 of container generate a conical surface which has a horizontally disposed axis. The feed end of container 10 moves in an orbit in a generally vertical plane and the discharge end of container 10 moves in a smaller orbit in a generally vertical plane.

In the embodiment of the invention illustrated the apex of the generated conical surface would be to the right of the discharge end of the mill outside the physical limits of the space within container 10. As the effective weight of Weight means 33 is decreased relative to weight means 32, the apex of the conical surface moves to the left toward bearing 23. If no unbalanced weight were provided at the discharge end of the mill, for example, the apex of the conical surface would be in the vicinity of bearing 23. As any suitable mounting arrangement for permitting the axis of shaft to generate a conical surface is satisfactory, a stationary bearing housing for bearing 23 which allows pivotal movement of rotatable shaft 25 at that point would be suitable.

The present inventor has discovered that when a mill constructed as described herein is operated with a mixture of balls of different sizes, a segregation of the balls occurs in which the larger balls tend to accumulate at the feed end of the mill, where the amplitude of vibration is the greatest, and the smaller balls accumulate at the discharge end where the amplitude is the smaller. A segregation of grinding balls 44 as contemplated by this invention is shown in the drawing. The advantage of this segregation of the grinding balls is that a more efficient grinding action is obtained. When the material to be ground first com-es into contact with the larger balls at the feed end of the mill, the relatively larger pieces of material are reduced in size. As the material to be ground advances longitudinally through the mill and comes in contact with the smaller balls at the discharge end of the mill, a finer grinding of the material is effected.

When a mill described herein is operated the grinding balls become smaller in size due to wear and the total weight of the ball charge is reduced accordingly. At intervals a batch of grinding balls of the largest size are added to the mill to compensate for the loss of weight of the ball charge due to the wear to which the individual grinding balls are subjected. The grinding balls added to the ball charge tend to accumulate at the feed end of the mill where the amplitude of vibration is the greatest and the worn grinding balls, which originally were of the largest size, tend to accumulate at the discharge end of the mill where the amplitude of vibration is smaller than at the feed end of the mill. The supplying of a batch of grinding balls of the largest size at intervals results in there being a gradation with regard to the sizes of the grinding balls in the mill at all times.

While only one embodiment of the invention is described and illustrated herein, it is to be understood other embodiments and modifications of the invention may be made and used without departing from the spirit and scope of the invention as set forth in the appended claims.

it is claimed and desired to secure by Letters Patent:

1. A grinding mill comprising a generally horizontal non rotatable container having an arcnate bottom portion and having a feed opening at one end adjacent the upper part of said container and a discharge opening at the other end of said container, means resiliently supporting said container for vibratory movement, power driven rotary means mounted on said container including eccentrically disposed weight means at opposite ends of said container with the weight means at the feed end of said container having a larger moment of inertia than the weight means at the discharge end of said container, and a plurality of loose grinding bodies of graduated sizes in said container.

2. A grinding mill comprising a container having two end walls and a generally cylindrical connecting shell, means supporting said container for vibratory movement relative to a stationary support with the longitudinal axis of said cylindrical shell in a substantially horizontal position, inlet means at one end of said container and discharge means at the other end thereof, a rotary power driven mechanism journaled in said container and extending longitudinally thereof, said mechanism including a first unbalanced weight at the feed end of said container and a second unbalanced weight at the discharge end of said container having a smaller moment of inertia than said first weight, and resilient means supporting said container so that a conical motion of said container is effected as a result of rotation of said mechanism.

3. A grindnig mill comprising a container having a pair of spaced end walls with an inlet opening adjacent one of said end walls and an outlet opening adjacent the other of said end walls, means resiliently supporting said container for vibratory movement relative to a stationary support, a charge of grinding media of various sizes in said container, bearing means connected to each of said end walls, a rotatably driven shaft extending through said container and journaled in said bearing means, eccentric weight means attached to opposite ends of said shaft outward of said end walls, said weight means at said feed end having a greater moment of inertia than said weight means at said discharge end of said container so that rotation of said shaft vibrates said container and said shaft moves in a path that traces a cone having its apex outward of the discharge end of said container.

4. A grinding mill comprising a container having a generally cylindrical shell enclosed by a pair of spaced end walls with an inlet opening adjacent one of said end walls and an outlet opening adjacent the other of said end walls, means resiliently supporting said container for vibratory movement relative to a stationary support, a cylinder extending through said container and both of said end walls to define with said end walls and said shell an annular grinding space around said cylinder, a charge of grinding media of various sizes in said grinding space, bearing means connected to each of said end walls coaxial with said cylinder, a rotatably driven shaft 'extending through said cylinder and journaled in said hearing means, eccentric weight means attached to opposite ends of said shaft outward of said end walls, said weight means at said feed end having a greater moment of inertia than said weight means at said discharge end of said container so that rotation of said shaft vibrates said container and said shaft moves in a path that traces a cone having its apex outward of the discharge end of said container.

References Cited in the file of this patent UNITED STATES PATENTS 2,230,325 Haver Feb. 4, 1941 2,292,275 Kiesskalt Aug. 4, 1942 2,298,015 Lincoln Oct. 6, 1942 FOREIGN PATENTS 45,711 Netherlands May 15, 1939 494,311 Great Britain Oct. 24, 1938 896,445 Germany Nov. 12, 1953 

